The design rule of a semiconductor integrated circuit is continuously being shrinked, accompanied by the performance deterioration due to wiring delay which is becoming prominent. That is, a wiring signal delay of a semiconductor integrated circuit is determined by a wiring CR time constant (C: wiring capacity, R: wiring resistance). Because of the increase in wiring resistance due to the decrease in a wire width and the increase in a capacity due to the decrease in a gap between wires, there is a danger that the wiring CR time constant may not catch up with the improvement in switching speed of transistors. Conventionally, an aluminum alloy was mainly used as a wiring material of a semiconductor integrated circuit. However, a copper wiring has been used in an integrated circuit requiring high-speed operation for a purpose of decreasing the resistance in a wiring.
In order to reduce the capacitance between wirings, an insulation film material that has a lower dielectric constant than the currently used silica (SiO2) is beginning to be adopted. As an insulation film having a low dielectric constant, a fluorine-containing silica (SiOF), a porous silica, and an organic polymer film (organic insulation film) are known. The fluorine-containing silica is already being used in part of some products, however, if the fluorine concentration inside the film is increased for promoting a low dielectric constant of the film itself, the problem of corrosion of a wiring metal occurs with hydrofluoric acid generated from a reaction with moisture or hydrogen, or the problem of the increased dielectric constant occurs by desorption of fluorine. Furthermore, as the technology of the semiconductor integrated circuit progresses, the fluorine-containing silica film (SiOf) providing the dielectric constant of 3.3 can no longer meet the requirement of the insulation film. The insulation film that does not contain fluorine and has the dielectric constant of 3 or less is in high demand as the interlayer insulation film of the multi-layer wirings. As one of the candidates, the organosiloxane copolymer film having excellent properties both in heat and moisture resistance has been in urgent demand for development. Conventionally reported methods of forming the organosiloxane copolymers are broadly classified to the spin coating method and the CVD method.
1. First Related Art
In the spin coating method, a raw material organosiloxane monomer is dissolved in an organic solvent. The spin-coated film is formed, the solvent is removed during the film formation, the organosiloxane monomer inside the coated film is heated, and a polymerization reaction of the monomer proceeds. Consequently, a two-dimensional or three-dimensional network structure polymer film is formed by the thermal polymerization reaction. A backbone configuring the organosiloxane copolymer film which is the product, depends on the structure of the organosiloxane monomer dissolved in the organic solvent.
For example, according to “REAL-TIME FT-IR STUDIES OF THE REACTION KINETICS FOR THE POLYMERIZATION OF DIVINYL SILOXANE BIS BENZOCYCLO BUTENE MONOMERS” (material Research Symposium Proceeding vol, 227, p, 103, 1991), by T. M. Stokich, Jr., W. M. Lec, and R. A. Peters discloses the method of forming an organosiloxane polymer film. After dissolving a divinylsiloxane-bisbenzocyclobutene (BCB-DVS) monomer which is one type of the straight-chain siloxane in a mesitylene which is spincoated, the mesitylene in the solvent is removed by baking at 100 degrees Celsius, and the residue was further heated up to 300 degrees Celsius to 350 degrees Celsius to obtain the organosiloxane polymer film. A divinylsiloxane-bisbenzocyclobutene monomer, as shown in chemical formula (1) below, is an organosiloxane monomer that includes 2 vinyl groups and 2 cyclobutene groups which are unsaturated hydrocarbon chains, and the straight-chain siloxane. Its thermal polymerization reaction is progressed as follows.
Chemical Formula (1): divinylsiloxane-bisbenzocyclobutene
First of all, accompanied by the reaction of chemical formula (2) shown below, the cyclobutene group inside the divinylsiloxane-bisbenzocyclobutene monomer undergoes thermal ring-opening polymerization reaction by thermal energy, and changes to 2 vinyl groups (methylene groups).
Chemical Formula (2): Ring-Opening Reaction of Benzocyclobutene Group
Accompanied by the reaction of chemical formula (3) shown below, 2 vinyl groups (methylene groups) react to another vinyl group inside the BSB-DVS monomer to form the 6-membered hydrocarbon (dihydronaphthalene) so that the polymerization reaction is generated. From this reaction path, a dimer that connects 2 BSB-DVD shown in chemical formula (4) below, is obtained.
Chemical Formula (3): Addition Polymerization Reaction of Vinyl Group and Open-Ring Group of Benzocyclobutene Group.
Chemical formula (4): divinylsiloxane-bisbenzocyclobutene Dimer
Inside the dimer of BCB-DVS to bc synthesized, 3 unreacted benzocyclobutenes and 3 vinyl groups remain. That is, at least 6 BCB-DVS monomers and the dimer may further undergo addition polymerization. If a mobility of the divinylsiloxane-bisbenzocyclobutene is sufficiently large, then a complex and intricate polymer film where the BSB-DVS are bridged to one another is formed as shown in chemical formula (5).
Chemical Formula (5): Organic Polymer Film Synthesized by Addition Polymerization of divinylsiloxane-bisbenzocyclobutene (BSB-DVS)
However, as for the polymer formation by using the spin coating method, a BSB-DVS monomer is being dissolved in a solvent, but, if the monomer concentration increases accompanied by the evaporation of the solvent, the viscosity is increased, and the monomer mobility gets less. In other words, although there are total of 4 sites available for addition polymerization in the BSB-DVS monomer itself, it can only bond to a few BSB-DVD nearby. Because of this, the polymer formation by using the spin coating method cannot attain a sufficient bridge density. Incidentally, there was a problem of deterioration in thermal resistance of the obtained polymer film, and a problem of decline in the film strength. Furthermore, the spin coating method in this case dissolves the organic monomer to a solvent, and the dissolved solid is spin coated. However, the spin coating process has a drawback that the yield of the starting raw material is low because about 90% of the dissolved material is scattered from the substrate. Moreover, the method of heating a spin-coated film in a baking furnace thereby to remove a solvent beforehand, and further heated at high temperature to cause the polymerization reaction of the organic monomer thereby forming an organic polymer film. At this time, when oxygen is present in the baking furnace, the organic polymer film having the desired characteristics is not obtained sometimes by the reaction of oxygen with a portion of the organic monomer. To prevent that from happening, for example, the atmosphere in the whole baking furnace is effectively replaced by a nitrogen gas, however, it is difficult to realize that at a low cost. Furthermore, since the dissolved oxygen in the solvent had sometimes reacted with the organic monomer during baking, a strict atmosphere control is required throughout the whole process, but it is practically difficult to carry out the strict atmosphere control in the spin coating method. Although the spin coating is conducted in a locally evacuated spin coating chamber to prevent scattering of the volatile solvent in the working environment, there is also a risk of contamination of the spin-coated film with floating dust particles or fine particles of the dried organic monomer adhered to the inner wall of the spin coating chamber. In this case, the film quality is deteriorated. Furthermore, the spin coating also has a problem that the environmental burden is large because a large amount of organic solvent is required and the amount of evaporation is also large.
(Second Prior Art)
Japanese unexamined patent publication No, HEI 11-288931 discloses a plasma CVD method using as a raw material a single vaporized gas which is the silicon type hydrocarbon compound where the saturated hydrocarbon is bonded to the straight-chain siloxane (—Si—O—Si—), for obtaining the silicon type organic insulation film with the dielectric constant of 3 or less. By adjusting the FR power or the deposition pressure during the plasma polymerization, although the composition ratio of elements such as carbon, hydrogen, silica and oxygen inside the synthesized organosiloxane film can be controlled, however, the molecular backbone structure of the obtained organosiloxane film or the polymerization structure of the whole film cannot be controlled.
(Third Prior Art)
Published Japanese translations of PCT international publication for patent application No. 2002-503879 (hereinafter referred to as literature 3) discloses a technique to form the organosiloxane film by reacting the oxidized gas eliminated by using a low-powered plasma with the organosilicone compound monomer (organosiloxane monomer) composed of the saturated hydrocarbon group and the siloxane. This reaction process does not have the polymerization selectivity such as activating a specific hydrocarbon group in the organosiloxane monomer and bonding to a specific site and an oxidizing agent gas. Accordingly, when oxidizing the organosiloxane monomer inside the plasma, it was difficult to strictly control its oxidation reaction or its degree of oxidation. In other words, it was difficult to design molecules of porous film by inducing minute pores to the silicone type organic insulation film. Furthermore, in order to improve the deposition property of the silicone organic insulation film synthesized as the lower and upper layers, it was necessary to control the composition of organosiloxane film near to the interface. According to the disclosed organosiloxane film formation method, it does not have the means for controlling the molecular structure or the chemical composition of the intermediate layer or the composition near to the interface. The present inventors have developed the technology to form the organosiloxane film on the substrate surface by vaporizing the organosiloxane monomer including an unsaturated hydrocarbon group, transporting it through the vapor using a carrier gas, and spraying to the heated substrate surface via the He plasma formed in the reaction chamber. This relating technology is disclosed in Japanese unexamined patent publication No. HEI 2000-12532. According to this organosiloxane film formation method, a vapor-transported organoxiloxane monomer generates the polymerization reaction on the substrate surface, and the organosiloxane film is formed. For example, if divinylsiloxane-bisbenzocyclobutene (BCB-DVS) monomer is utilized shown in chemical formula (1), having the straight-chain organosiloxane as backbone, its plasma polymerization reaction process is assumed to coincide approximately to the thermal polymerization reaction, and the cyclobutene group and the vinyl group which are the unsaturated hydrocarbon groups included in the organosiloxene are selectively activated, and the organosiloxane film having an intricate bridge structure shown in the chemical formula (5) is obtained, by the polymerization reaction via the elementary reaction processes shown in the chemical formulae (2) to (4).
The key point of this technology is in the fact that the unsaturated hydrocarbon group such as cyclobutene group or vinyl group is included in the organosiloxene monomer used as a raw material, and the organosiloxene monomers are bonded in a network shape via these unsaturated hydrocarbon groups. In other words, by controlling the position of the unsaturated hydrocarbon groups taking part in the polymerization reaction, the position of the polymerization reaction is specified, and a network structure of the desired organosiloxane film with organosiloxane monomer backbone is formed. Since the organosiloxane monomer supplied as a vapor is in high vacuum, in comparison to the spin coating method, its mobility is large on the surface, and the film strength and the thermal resistance of the obtained organosiloxane film are increased by improving the bridge density of the network structure. For example, as for the organosiloxane film obtained from the BCB-DVS monomer by the plasma polymerization, it has a highly dense bridge structure of the straight-chain siloxanes via the unsaturated hydrocarbon, and its dielectric constant is ranging from 2.5 to 2.7.
Particularly, in the case of using it as the interlayer insulation film of the multi-layered wiring of ULSI, the organosiloxane film structure is formed in between the upper wiring layer and lower electrode layer. At this time, other insulation film is used in the production of the lower electrode layer and the upper wiring layer. Accordingly, the organosiloxene film of the interlayer insulation film is of a laminated structure with the organic or inorganic insulation film of the upper layer and lower layer. Because of this, it is necessary that the film strength and the deposition property of the insulation film at the interface contacting the upper plane or the lower plane of the organosiloxane film to be high. To improve the film strength near to the interface or the deposition property of the organosiloxane film, it is effective to increase its bridge density but that accompanies the increase in the dielectric constant.
Ideally, the organosiloxene film utilized as the interlayer insulation film, has a high strength film quality and a high bridge density which is excellent in the deposition property only near to the interface with other film material. Other section of the interlayer other than the interface ideally has a film configuration that keeps a bridge density that can attain the appropriate dielectric constant. However, as for the plasma polymerization film utilizing the single organosiloxene monomer as the raw material, it was generally difficult to arbitrarily select the bridge density of the obtained polymer film in the film thickness direction to make the polymer film with the continuously changing deposition property and dielectric constant. That is, in the plasma polymer film using the conventional single raw material, it was impossible to arbitrarily control the bridge density for controlling the film quality to a large extent and continuously in the film thickness direction.